METAL & GOLD CROWNS

The use of gold as a restorative material has a long history of durability and strength. A gold crown permits a more conservative crown preparation as only a thin layer of gold alloy is required for strength. It is extremely gentle on the opposing teeth and a great option for molars in patients who have a clenching or grinding habit. However, due the unaesthetic colour its use is often limited to the back teeth. Because a gold crown is an alloy, whereby the gold is mixed with other metals to improve strength, some patients may experience sensitivity. To counteract an allergy, the use of a high noble alloy where at least 60% of crown is made of gold and other precious metals is advisable.

Patients with gold restorations may experience some sensitivity to hot and cold food or drinks during the first several weeks after placement of the crown due to metal conductivity. In general, this sensitivity subsides over time and is often less sensitive than porcelain bonding techniques.

PORCELAIN & CERAMIC CROWNS

If you are looking for a natural cosmetic option then use of a porcelain crown is the best option. Porcelain does not conduct heat or cold efficiently so post-operative sensitivity is less than gold crowns. However, they are bonded to teeth differently than gold and some people may be more sensitive to these bonding procedures.

Porcelain is harder than natural tooth so can wear down opposing natural teeth, especially in patients with a grinding or clenching habit. Porcelain is also brittle and can be prone to fracturing if it is too thin or there is too much flexing due to a traumatic bite. To provide the necessary strength to prevent fractures, the porcelain crown needs to be thicker than a gold crown, which means removal of more tooth structure.

·  Porcelain Fused to Metal

An outer layer of porcelain is fused to a metal substructure made of gold or metal alloy. The combination of both materials provides a compromise between the strength of gold and cosmetic benefits of porcelain. Porcelain bonding processes can be avoided with the crown cemented the same way a gold crown would be. However, the drawback is the metal substructure creates an opacity which makes the tooth less natural, and if there is gum recession, the metal substructure may become visible at the gum line.

·  Porcelain fused to Zirconia core or full zirconia

Zirconia is a white crystalline oxide derived from the metal zirconium and in its cubic form it creates cubic zirconia, diamond like stones. Zirconia is very strong and durable.

Zirconia can be used as a full thickness crown or layered with a Zirconia base substructure and an outer Porcelain layer. The bonding process between zirconia and porcelain is stronger than with porcelain and gold. We can use metal based cements that are less sensitive than porcelain bonding techniques.

The use of Zirconia as a base or full thickness offers a better cosmetic result than a metal base. However those with metal sensitivities may not be suitable for Zirconia.

COMPOSITE CROWN

A cheaper alternative to a porcelain or metal crown is a crown made of composite; a synthetic resin material filled with silica often used for white fillings. It is the least favourable option in regards to strength and durability compared to porcelain and gold but ideal for patients with metal/porcelain sensitivity or as a cheaper alternative. Composite is softer than porcelain, wears at the same rate as natural teeth and is chemically bonded to the tooth.

The composite resin crown can either be handcrafted directly or indirectly.

Direct Composite Crown:

The composite crown is built up in layers directly onto the tooth, handcrafted by your dentist and shaped so that it fulfils both appearance and functional purposes.

Indirect Composite Crown:

The composite crown is custom made outside the mouth and then bonded onto the tooth

• Using a dental technician: An impression of the prepared tooth is taken, a temporary crown fitted. And the crown made in the laboratory by a skilled dental technician
• CAD/CAM: A composite crown can be made stronger if it is cured and processed into blocks outside the mouth and then milled to fit using CAD/CAM techniques like CEREC. An optical impression, using a camera, is taken of the prepared tooth and converted by software into a 3D virtual model on the computer screen. A ceramic block is then inserted into a milling machine to create the crown.
• Using the One Visit Crown: The OVC is a generic hybrid dental crown made of ceramic infused with composite resin carefully designed by the clever team at Rhondium in Katikati. The tooth is prepared, the old fillings removed, and then the OVC shaped and cemented into your mouth.  The One Visit Crown (OVC) is, as the name suggests, done in one visit, saving you time and money.

TEMPORARY CROWN

Temporary crowns, often made of acrylic or stainless steel, are often placed for approximately two weeks whilst a dental technician is creating your crown. They may also be placed on decayed baby teeth to prevent further decay and maintain the space until the tooth is exfoliated. They are not as durable as permanent crown options.

WHAT TO EXPECT IN THE APPOINTMENT

The existing filling and tooth is shaped and reduced in height to allow room for the crown to fit. Often all the old filling is removed first to check there is no decay or undermining hairline fractures. A core of dental material using composite tooth coloured material or silver coloured amalgam material is formed. If you are having a direct crown made, it will be cemented in the same appointment. If using an indirect option, moulds and models of the teeth are taken along with the shade of the tooth, and sent to a local technician who will construct the crown, in the meantime a temporary crown will be fitted. After the crown returns from the technician it is cemented into place, usually two weeks after the initial appointment.

All restorations in the mouth have the potential to develop decay at the margins or may need to be re-cemented as the teeth flex with use. Any tooth that has a crown placed, may also develop the need for a root canal.

DENTAL BRIDGE

A bridge is a series of crowns used to fill a gap when a tooth or teeth are lost. At either side of the missing tooth, the teeth are crowned, these anchor teeth are called abutment teeth. Joined in between the abutments is a pontic or a tooth replacing the missing tooth. The pontic is the crown in the space that joins or ‘bridges’ the crowned abutments. The bridge can be made of gold, porcelain, zirconia or a combination of materials.